Failure detecting system and method for automatic transmission

Abstract: In case where an engine rotational detection signal from an ignition pulse generator is not appropriately detected even if an amount of induction air and a fuel injection amount are larger than predetermined values, an engine rotational signal failure is decided, and an automatic transmission is controlled in a state before the decision. Thus, the automatic transmission control can be executed based on the engine rotational speed. In case where a failure of the cruise control set signal line is detected, the automatic transmission control based on the cruise control is prohibited. The normal state is recovered when an off signal of the cruise control set is detected in the above-described conditions. Accordingly, since a failure of the cruise control set signal line is reliably detected, the automatic transmission control is appropriately executed by using the cruise control signal. Thus, the automatic transmission control can be executed based on a cruise control signal.

Description: The present invention relates to a failure detecting system for an automatic transmission of a vehicle employing an engine rotational speed, a cruise control signal, a brake signal from a brake switch or a shift range switch operation signal from a shift range switch as one of control signals to control the automatic transmission. An automatic transmission AT is fundamentally controlled to be shifted by regulating depression of an accelerator pedal and a traveling speed of a vehicle. Accordingly, in case where the vehicle travels in a drive (D) range, reduction gears can be shifted by positively depressing or releasing the accelerator pedal. In a conventional automatic transmission, for example, in a drive (D) range, an optimum gear is selectively controlled from a vehicle speed at that time and a throttle opening according to a shift map storing a predetermined shift schedule as shown in Fig. 6. As a lockup function of an automatic transmission a lockup clutch is engaged when a vehicle speed becomes higher than a predetermined value in a certain gear position such as, for example, in a third gear or an overdrive (fourth gear), to directly couple an output shaft of a torque converter to an output shaft of an engine. In other cases, the lockup clutch is released to connect the input shaft of the torque converter to the output shaft of the engine. The lockup is released to utilize a function of the torque converter thereby to achieve smooth starting, smooth accelerating or smooth speed shifting without engine knocking or stop at the time of starting, abruptly accelerating, speed shifting the vehicle. However, in a state that a load is low and an engine rotational speed is high, the torque converter is locked up thereby to prevent loss of power due to a slip of the torque converter and hence to prevent a increase in fuel consumption. A cruise control unit so controls an opening of a throttle valve as to maintain a certain vehicle speed set by a driver as a desired traveling speed thereby controlling in response to a road state. As the typical automatic transmission control to execute as described above, Japanese Utility Model Application Laid-Open 63-115558 discloses an internal combustion engine with an abnormality detector for judging an abnormality based on a rotational speed signal from a rotation detector for electrically detecting a rotational speed of the internal combustion engine and a fuel amount signal from a fuel amount detector for detecting a fuel supply amount to the internal combustion engine. In the above-described internal combustion engine with the abnormality detector, it is determined that an engine rotational speed signal line is on when an engine rotational speed is smaller than a predetermined value at a certain vehicle speed or more. However, even if an engine stop occurs at a certain vehicle speed or more, it is erroneously detected that the failure occurs at the engine rotational speed signal line. In such a case, it becomes impossible to detect a failure of an ignition pulse generating an engine rotational speed detection signal to be supplied to the engine rotational speed signal line. Furthermore, there are disadvantages that the automatic transmission control based on the engine rotational speed such as, for example, a gear shift control, a lockup control, a line pressure control can not be appropriately controlled. As the typical automatic transmission control to execute as described above, Japanese Utility Model Application Laid-Open 63-137038 discloses an automatic transmission controller in which hunting of the vehicle speed due to a gear shifting during a cruise control traveling is prevented and a fail-safe control is performed when an abnormality of an automatic transmission occurs. More specifically, the automatic transmission controller additionally provides a memory map storing a shift schedule for controlling the automatic transmission in response to a cruise control signal supplied from a cruise controller, in which map a hysteresis width is so set as to reduce the number of repetitions of down and up shifting. In this case, since the number of times of gear shifting during the cruise control is reduced, hunching of the vehicle speed due to the gear shifting can be prevented, and a riding comfort can be improved. In the conventional automatic transmission controller as described above, a vehicle can be traveled smoothly without shock in the case of shifting gear during the cruise control, but it does not have a fail-safe function in case where the cruise control signal is, for example, erroneously generated even though the cruise control is not performed by the cruise controller. Usually, the automatic transmission controller functions as a gear shifting control, a lockup control, an overrunning clutch control (namely, engine brake control), etc. Therefore, if a fail-safe function is not provided, these functions are erroneously operated when a cruise control signal is erroneously generated. In a conventional automatic transmission, for example, in a drive (D) range, an optimum gear is selected based on a vehicle speed and a throttle opening at that time, from a shift schedule map storing a predetermined shift schedule as shown in Fig. 6. Further, in such an automatic transmission control, detection signals from various detecting sensors are input to a controller to perform a lockup control, an overrunning clutch control, a line pressure control, an auto-pattern select control, a gear shift timing control, a transfer clutch control of four-wheel drive as well as the above-described gear shift control. JP-A-1-145234 discloses a cruise control of a vehicle using a brake switch signal. Furthermore, JP-A-63-34349 discloses a method for detecting a trouble of a gear position switch. That is, if a gear position switch does not generate an ON signal when a predetermined time is elapsed after a gear shifting is performed, it is returned to a position before the gear changing, and when the same operation as above is conducted predetermined times or more, the switch is decided to be a trouble. However, in the above-described conventional method for detecting the trouble of the gear position switch, in case where the ON signal is not generated from the gear position switch, the gear is returned to the position before the gear shifting, and when the same operation as above is again conducted predetermined times or more, the switch is decided to be the trouble. Therefore, in the case of the trouble, it merely controls to return the position of the switch to the position before the gear shifting, an accurate automatic transmission control responsive to various traveling states of the vehicle is impossible. US-A-5 125 293 relates to an adaptive correction of servo activating hydraulic fluid pressure during shift. This system and method detects the failure of the intake air amount by using an airflow meter. An object of the present invention is to provide a failure detecting system for an engine rotational signal line connected to a controller for an automatic transmission of a vehicle which can reliably detect a failure of the engine rotational signal line thereby to appropriately control an operation of an automatic transmission control based on an engine rotational speed. This object is achieved with the features of the claims. According to the failure detecting system for the engine rotational speed signal line of the present invention, the automatic transmission control of the automatic transmission AT is prohibited in case where one of the following conditions is satisfied. More specifically, (1) When the amount of intake air is larger than a predetermined value, the state that the engine rotational speed is smaller than a predetermined value is continued for a predetermined time. (2) When the vehicle speed is larger than a predetermined value, the amount of intake air is larger than a predetermined value and the state that the engine rotational speed is smaller than a predetermined state is continued for a predetermined time. (3) When the fuel injection amount is larger than a predetermined value, the state that the engine rotational speed is smaller than a predetermined value is continued for a predetermined time. (4) When the vehicle speed is larger than a predetermined value, the fuel injection amount is larger than a predetermined value and the state that the engine rotational speed is smaller than a predetermined value is continued for a predetermined time. In case where any of the above conditions (1) to (4) is satisfied, it is determined that a failure occurs on the engine rotational speed signal line, whereby the automatic transmission control based on the engine rotational speed is prohibited, and the state before the failure is detected is maintained. The nature, utility, and further features of this invention will be understood from the following detailed description with respect to preferred embodiments of the invention by referring the accompanying drawings, briefly described below. In the accompanying drawings: Fig. 1 is a block diagram showing a failure detecting system for an automatic transmission of a vehicle employing an engine rotational speed according to an embodiment of the present invention; Fig. 2 is a flow chart for explaining an example of the operation of a failure detecting system for an engine rotational speed line according to Fig. 1; Fig. 3 is a flow chart for explaining an example of the operation of a failure detecting system for an engine rotational speed line according to Fig. 1; Fig. 4 is a flowchart for explaining an example of the operation of a failure detecting system for an engine rotational speed line according to Fig. 1; Fig. 5 is a flow chart for explaining an example of the operation of a failure detecting system for an engine rotational speed line according to Fig. 1; Fig. 6 is a view showing a shift schedule stored in a gear shift map for a conventional automatic transmission control. The embodiment of the present invention will be explained with reference to accompanying drawings. Fig. 1 shows a control system according to an embodiment of a failure detecting system for an automatic transmission of a vehicle of the present invention. The control system employs an engine rotational speed as one of input signals to control the automatic transmission. A failure is detected on the engine rotational speed when conditions to be described later are satisfied. When the failure is detected, a transmission control based on the engine rotational speed is prohibited, and a state before the failure is detected is maintained. The controls based on the engine rotational speed includes, for example, a gear shift control, a lockup control, and a line pressure control. A throttle opening detection signal from a throttle sensor 11 and an ATF oil temperature detection signal from an ATF temperature sensor 12 are input to an input interface circuit 21 of an electronic control unit (ECU) 20 of the control system. The throttle opening detection signal from the throttle sensor 11 is used to determine a gear shifting point, a line pressure in a control circuit of the automatic transmission and a lockup vehicle speed for the lockup. The ATF oil temperature detection signal from the ATF temperature sensor 12 is used to prohibit lockup at the time of a low temperature and to release a fourth gear. Various detection signals input through the input interface circuit 21 are converted to digital signals through an A/D converter 22, and then fed to a CPU 24. A program for executing a predetermined calculation of the CPU 24 is stored in a memory 24a associated with the CPU 24. A vehicle speed detection signal from a vehicle speed sensor 13, an engine rotational speed detection signal from an ignition pulse generator 14, a shift range signal from an inhibitor switch 14, and a throttle full close state detection signal from an idle switch 16, an ABS signal from an ABS control unit 19a, a cruise control signal from a cruise control unit, and a brake switch signal from a brake switch 19 are input to an input interface circuit 23. The vehicle speed detection signal from the vehicle speed sensor 13 is used to control a gear shifting, lockup, line pressure and transfer. The engine rotational speed detection signal from the ignition pulse generator 14 is used to smoothly control the lockup operation and to prevent overrunning of an engine in a "1", "2" or "3" range. The shift range signal from the inhibitor switch 15 is used to determine the line pressure. The throttle full close state detection signal from the idle switch 16 is used to release a lockup clutch and to control the line pressure. An output of the CPU 24 is applied to an output interface circuit 25 for controlling ON/OFF of shift solenoids (1)31, (2)32, (3)33 and an output interface circuit 26 for controlling duty ratios of duty solenoids (A)34, (B)35 and (C)36. The shift solenoids (1)31, (2)32 control gear shifting, especially, its timing, thereby reducing a gear shifting shock. The shift solenoid (3)33 controls an overrunning clutch and a timing of shifting from a third gear to a second gear. The timing control reduces a shock at the time of shifting down the speed, and the overrunning clutch is operated at the time of decelerating, thereby effecting an engine brake. The duty solenoid (A)34 regulates the line pressure to an optimum pressure responsive to a driving state. The duty solenoid (B)35 smoothly engages or disengages the lockup clutch. The duty solenoid (C)36 regulates a hydraulic oil pressure of a transfer clutch to control the rear wheel drive force. The operation of the automatic transmission control system described above will be explained by referring to Fig. 2. Fig. 2 shows a flow in case that an amount of engine intake air is used to detect a failure of the engine rotational speed detection signal. When an air amount detection signal from an air flow sensor 17 is input to the CPU 24 of the ECU 20, whether or not an amount of intake air is larger than a predetermined value is judged (in a step 201). When it is judged that the amount of induction air is larger than a predetermined value, whether or not an engine rotational speed based on the engine rotational detection signal from the ignition pulse generator 14 is smaller than a predetermined value is judged (in a step 202). If it is judged that the engine speed is not smaller than a predetermined value, it is normal. A failure flag set, for example, to a register (not shown) provided in the CPU 24 is cleared, and a timer (not shown) in the CPU 24 is set to a predetermined time (in steps 203 and 204). Moreover, when it is judged that the engine rotational speed is smaller than the predetermined value (in the step 202) and a state that the engine rotational speed is smaller than the predetermined value continues for more than the predetermined time is further judged (in a step 205), a failure flag is set to the register (not shown) (in a step 206). Thus, the failure flag is set to prohibit an automatic transmission control based on the engine rotational speed (in a step 207), and it is controlled to maintain the previous state before the engine rotational signal failure is judged. On the contrary, if the state that the engine rotational speed is smaller than the predetermined value continues for more than the predetermined time is not judged (in the step 205), a failure is not detected, and the automatic transmission based on the engine rotational speed is continued. Fig. 4 shows a flow in case where the amount of intake air of a decision condition is replaced with a fuel injection amount. First, whether or not the fuel injection amount is larger than a predetermined value is judged (in a step 401). Then the predetermined value of the fuel injection amount is calculated based on the intake air amount detection signal from the air flow sensor 17, and compared with an actual injection pulse width to the injection, thereby judging the fuel injection amount. In case where it is judged that the fuel injection amount is larger than the predetermined value, it is judged that the engine rotational speed indicated by the engine rotational detection signal from the ignition pulse generator 14 is smaller than a predetermined value (in a step 402). If it is judged that the engine rotational speed is not smaller than the predetermined value, it is normal, a failure flag set, for example, to a register (not shown) provided in the CPU 24 is cleared and a timer (not shown) in the CPU 24 is set to a predetermined time (in steps 403 and 404). Moreover, when it is judged that the engine rotational speed is smaller than the predetermined value (in the step 402) and a state that the engine rotational speed is smaller than the predetermined value for more than a predetermined time (in a step 405), a failure flat is set to the register (not shown) (in a step 406). Thus, the failure flag is set to prohibit the automatic transmission control based on the engine rotational speed (in a step 407), and the state before the engine rotational speed failure is detected is maintained to be controlled. On the contrary, in case where the state that the engine rotational speed is smaller than a predetermined value is not continued for the predetermined time (in the step 405), it is not decided to be failure, and the automatic transmission control based on the engine rotational speed is continued. In the embodiment described above, the case where the amount of intake air and the fuel injection amount are larger than predetermined values is employed as one factor of the decision condition. However, the present invention is not limited to the particular embodiment. For example, as shown in Figs. 3 and 5, a vehicle speed detected by the vehicle speed sensor 13 may be added to the decision condition. More specifically, summary of flows of the case where the above-described factors are employed as decision conditions is as follows. (1) When the amount of engine intake air is larger than a predetermined value, the state that the engine rotational speed is smaller than a predetermined value is continued for a predetermined time. (2) When the vehicle speed is larger than a predetermined value, the amount of intake air is larger than a predetermined value and the state that the engine rotational speed is smaller than a predetermined state is continued for a predetermined time. (3) When the fuel injection amount is larger than a predetermined value, the state that the engine rotational speed is smaller than a predetermined value is continued for a predetermined time. (4) When the vehicle speed is larger than a predetermined value, the fuel injection amount is larger than a predetermined value and the state that the engine rotational speed is smaller than a predetermined value is continued for a predetermined time. In case where any of the above conditions (1) to (4) is satisfied, it is determined that a failure occurs on the engine rotational speed signal, the automatic transmission control based on the engine rotational speed is prohibited, and the state before the failure of the engine rotational speed signal is detected is maintained. In the embodiment described above, in case where the amount of intake air or the fuel injection amount is larger than predetermined value, when the engine rotational speed detection signal from the ignition pulse generator 14 is not suitably detected, a failure is determined, and the automatic transmission control is executed in the state before the failure is determined. Therefore, since the failure of the engine rotational speed signal can be reliably detected, the automatic transmission control based on the engine rotational speed such as, for example, a speed shift control, a lockup control, a line pressure control can be appropriately controlled.

Claims: A failure detecting system for an automatic transmission of a vehicle employing an engine rotational speed as one of control signals to control said automatic transmission, the system comprising: engine speed detecting means for detecting said engine rotational speed; air amount detecting means for detecting an amount of induction air; and transmission control prohibiting means for prohibiting a transmission control characterized in that said transmission control is based on said engine rotational speed, when said amount of induction air detected by said air amount detecting means is larger than a predetermined value, and when said engine rotational speed detected by said engine speed detecting means continues to be smaller than a predetermined value for more than a predetermined time. A failure detecting system for an automatic transmission of a vehicle employing an engine rotational speed as one of control signals to control said automatic transmission, the system comprising: engine speed detecting means for detecting said engine rotational speed; and transmission control prohibiting means for prohibiting a transmission control characterized by fuel injection amount detecting means for detecting a fuel injection amount, wherein said transmission control is based on said engine rotational speed, when said fuel injection amount detected by said fuel injection amount detecting means is larger than a predetermined value, and when said engine rotational speed detected by said engine speed detecting means continues to be smaller than a predetermined value for more than a predetermined time. A system according to claim 1 or 2, further comprising vehicle speed detecting means for detecting a vehicle speed, wherein said transmission control prohibiting means prohibit a transmission control, when said vehicle speed detected by said vehicle speed detecting means is larger than a predetermined value. A method for detecting a failure of an automatic transmission for a vehicle employing an engine rotational speed as one of control signals to control said automatic transmission, comprising the steps of: detecting said engine rotational speed; detecting an amount of induction air; and prohibiting a transmission control characterized in that said transmission control is based on said engine rotational speed, when said amount of induction air is larger than a predetermined value, and when said detected engine rotational speed detected by said engine speed detecting means continues to be smaller than a predetermined value for more than a predetermined time. A method for detecting a failure of an automatic transmission for a vehicle employing an engine rotational speed as one of control signals to control said automatic transmission, comprising the steps of: detecting said engine rotational speed; and prohibiting a transmission control characterized by further detecting a fuel injection amount, wherein said transmission control is based on said engine rotational speed, when said detected fuel injection amount is larger than a predetermined value, and when said engine rotational speed detected by said engine speed detecting means continues to be smaller than a predetermined value for more than a predetermined time. A method according to claim 4 or 5, further comprising comprising the steps of: detecting a vehicle speed and prohibiting a transmission control, when said detected vehicle speed is larger than a predetermined value.

Inventors: SAKAKIYAMA RYUZO, SHIRAKAWA KIMINAGA, TEZUKA KAZUNARI, SAKAKIYAMA, RYUZO, SHIRAKAWA, KIMINAGA, TEZUKA, KAZUNARI
Applicants: FUJI HEAVY IND LTD, FUJI JUKOGYO KABUSHIKI KAISHA
Application year: 1994
Main classification: F16H61
IPC codes: F16H59, F16H63, B60K31, B60T17, F16H61, B60W50